You know that you can own shotguns and rifles in the UK don't you?
Well, that's the short version. The long version is (from Wiki):
"Single-barrelled, double-barrelled shotguns, or those with a lever-action or, pump-action, or semi-automatic and fixed magazine capacity of no more than three (2 in the magazine and one in the chamber) cartridges are permitted on a Shotgun Certificate. Shotguns with a detachable magazine or larger fixed magazine are permitted on a Section 1 Firearms Certificate. Certain types of shotgun ammunition, such as rifled slugs and larger shot sizes can only be bought following the grant of an FAC (firearms certificate). There is no limit on the amount of guns or ammunition that a SGC (shotgun certificate) holder can acquire or possess at one time, although each shotgun is recorded on the certificate."
A Section 1 Firearms Certificate is basically a permission slip, which has to be approved by the police ("may issue", which means it's up to their discretion), of the exact type/caliber/number of a firearm you intend to purchase along with a specific usage for that firearm ("self-defense" or "because guns are cool" aren't valid reasons). Slugs and larger shot size ammunition require another certificate, in which the type and amount of ammunition you purchase has to be logged. Storage requirements for firearms and ammunition are also very specific and regulated.
For rifles:
"British law defines a "rifle" as a rifled firearm with a barrel longer than 30 cm, and a total length longer than 60 cm that does not fall under the classification of long-barrelled revolver or pistol. Single-shot, bolt-action, Martini-action, lever-action (also called under-lever action) and revolver rifles and carbines are permitted, with certificate, in any calibre. Self-loading (also known as semi-automatic) or pump-action rifles are only permitted in .22 rimfire calibre."
No semi-automatic rifles are allowed in calibers larger than .22 rimfire.